Flexible, multilayered transfer tape

ABSTRACT

A flexible, multilayered transfer tape is described which contains an auxiliary support, a layer of pressure-sensitive adhesive and a binder containing a white-pigmented transfer layer having greater adhesion to the pressure-sensitive adhesive layer than to the auxiliary support. The transfer layer, which contains a binder in addition to a white pigment, is present between the auxiliary support and the pressure-sensitive adhesive layer. The transfer tape is characterized in that a non-white pigment is present in finely dispersed form in either or both of a polymer-bonded interlayer and the pressure-sensitive adhesive layer. The polymer-bonded interlayer may be situated between the white-pigmented transfer layer and the pressure-sensitive adhesive layer or in the white-pigmented transfer layer itself. Such transfer tapes have significantly improved covering capacity as compared to transfer tapes in which only the white-pigmented transfer layer is tinted.

[0001] This invention relates to a multilayer flexible transfer tapecomprising an auxiliary support and a layer of pressure-sensitiveadhesive, a binder-containing white-pigmented transfer layer showinggreater adhesion to the layer of pressure-sensitive adhesive than to theauxiliary support being present between the auxiliary support and thelayer of pressure-sensitive adhesive, and to the use of this transfertape in roll form in a hand-held dispenser.

[0002] A transfer tape of the above- mentioned type is described inEP-A-0 318 804. According to this document, it is preferably used inroll form in a hand-held dispenser to enable the transfer layer to beapplied simply, quickly and uniformly to a substrate for covering errorsin texts or drawings and for making subsequent corrections. The transferlayer thus applied may then be written on, for example with writing inkor India ink.

[0003] In the case of the described transfer tape, it is of advantagefor the white-pigmented transfer layer to be darkened by theincorporation of black pigments, more particularly carbon black. Thecovering power of the transfer layer is improved in this way. However,the degree of darkening is limited insofar as, if the amount of blackpigment used is too large, the white appearance of the tape is impairedand can no longer be described as white. Overall, this solution is notsatisfactory.

[0004] Accordingly, the problem addressed by the present invention wasto further develop the transfer tape mentioned at the beginning in sucha way that the covering power of the transfer layer for the applicationin question would be improved without any serious effect on its“whiteness”.

[0005] According to the invention, the solution to this problem ischaracterized in that a non-white pigment is present in finely dispersedform

[0006] a) in a polymer-bonded interlayer situated

[0007] a1) between the white-pigmented transfer layer and the layer ofpressure-sensitive adhesive or

[0008] a2) in the white-pigmented transfer layer, and/or

[0009] b) in the layer of pressure-sensitive adhesive.

[0010] Overall, there are thus three versions of the multilayer flexibletransfer tape according to the invention. The version in which thenon-white pigment is finely dispersed in the layer b) ofpressure-sensitive adhesive is preferred. If, in individual cases, thedarker impression created when looking down onto the layer ofpressure-sensitive adhesive is undesirable, particularly when thenon-white pigment is a black pigment, such as carbon black, it is ofadvantage to use one of the two variants of version a).

[0011] The three versions of the transfer tape according to theinvention are described in more detail in the following with referenceto the accompanying drawings.

[0012]FIG. 1 shows a known transfer tape comprising an auxiliary support(1), a transfer layer (2) and a layer (3) of pressure-sensitiveadhesive.

[0013]FIG. 2 shows version a1) of the transfer tape according to theinvention. A polymer-bonded interlayer (4) containing a finely dispersednon-white pigment is present between the white-pigmented transfer layer(2) and the layer (3) of pressure-sensitive adhesive.

[0014]FIG. 3 shows version a2) of the transfer tape according to theinvention, in which the non-white-pigmented polymer-bonded interlayer is“sandwiched” by the white-pigmented transfer layer, i.e. thenon-white-pigmented interlayer (4) is present between the transfer layer(2) and an additional layer (2A) with the identical composition. Thefunction of the additional layer (2A) is to conceal the dark colorimpression created by the interlayer (4) when looking down onto atransparent layer of pressure-sensitive adhesive.

[0015]FIG. 4 shows version b) of the transfer tape according to theinvention in which a non-white pigment is finely dispersed in the layer(3A) of pressure-sensitive adhesive.

[0016] A “non-white pigment” in the context of the invention ispreferably a pigment which is substantially similar to the symbols, moreparticularly letters, to be covered. These are normally blue, black, redor green in color. In general, therefore, the color yellow should not beused. Black pigments, especially carbon black, are particularlypreferred in practical applications. Basically, the particle size of thepigments is not critical, although a particle size of about 1.5 to 0.005μm and, more particularly, of less than about 1 μm to colloidal particlesize is preferred. Fine-particle metal powders, more particularlyfine-particle aluminium, may be used instead of colored pigments. Thealuminium particles are preferably lamellar and have a thickness ofpreferably about 3 to 10 μm. They may be up to about 15 μm in lengthwithout any problems. Water-based aluminium pastes have proved to beparticularly suitable. Aluminium pastes such as these are produced by aspecial wet grinding process. A particularly preferred paste is marketedby Carl Schlenk AG under the name Aquasilber Aluminiumpaste LPW/1 380.

[0017] The interlayer and/or the pressure-sensitive adhesive layerpreferably contain(s) at least about 0.1% by weight of non-whitepigment, more preferably about 0.1 to 5% by weight and most preferablyabout 0.2 to 3.5% by weight of non-white pigment. If the quantity ofnon-white pigments used in both layers is below the limit of “less than0.1% by weight”, the desired effect cannot be obtained to the requiredextent. If, however, this quantity exceeds 5% by weight, no significantimprovement is obtained. If this limit is exceeded, for example inconnection with the layer of pressure-sensitive adhesive, the result mayeven be that the adhesiveness of this layer is adversely affected. Inorder to satisfy functional requirements, a quantity of about 3.5%should not be exceeded.

[0018] The transfer layer is “white-pigmented”. In other words, itcontains conventional white pigments in the quantity necessary toprovide the transfer layer with a certain covering power. White pigmentsof the type in question include in particular titanium dioxide (titaniumwhite) and precipitated chalk, alumina and/or colloidal silicas.According to the invention, however, there is nothing to prevent thetransfer layer being additionally toned down with suitable, differentlycolored pigments. This can be done by incorporating suitable quantitiesof black pigment, more particularly carbon black, and also by toningdown with other pigments, for example yellow and green. Toning down maybe necessary where the transfer layer is to be adapted to the color ofthe substrate on which the lettering, etc. is to be covered. Theobservations on the particle size of the “non-white pigments” againapply.

[0019] Thermoplastic or thermoelastic polymers are used in the form ofan aqueous solution or aqueous dispersion to form the binder-containingtransfer layer. The following substances are used with advantage tosolve the problem addressed by the invention:

[0020] a) polyurethanes with a molecular weight of 15,000 to 50,000, forexample Permuthane U 4924, a product of Stahl-Chemie, or Desmolac 2100,a product of Bayer AG,

[0021] b) linear saturated polyesters with a molecular weight of 20,000to 30,000, for example Vitel PE 307, a product of Goodyear Tire &Rubber, Polyflex 46962, a product of Morton,

[0022] c) styrene/isoprene/styrene copolymers, for example Clariflex TR1107, a product of Shell-Chemie,

[0023] d) acrylates and methacrylates, for example Plexigum 7 H, aproduct of Roehm, GmbH,

[0024] e) polyamides modified with diphenyl acid, for example Scope 30,a product of Rhône-Poulenc or Emerez 1533, a product of Emery Chemicals,

[0025] f) polymer dispersions based on vinyl propionate, for examplePropiofan 6D, a product of BASF, and

[0026] g) water-soluble carboxyfunctional polymethacrylate, for exampleRohagit SD15, a product of Roehm GmbH.

[0027] This list is by no means complete and does not represent anylimitation of choice. On the contrary, it is quite clear to the expertthat other binders may also be used, especially since the essence of theinvention does not lie in the type of binder used.

[0028] In order further to optimize the invention, the type ofplasticizer used should also be taken into account in choosing theparticular binder for forming the transfer layer. When the transferlayer is applied to the surface to be corrected or covered, theplasticizer should not penetrate through the normally thin layer ofpressure-sensitive adhesive and come into contact with the text/symbolsto be corrected or the pigments present there, which would result inunwanted coloring of the transfer layer. Conventional plasticizers, suchas silicone oil, castor oil and mineral oils, are suitable for thispurpose. Plasticizers preferably used in other fields of application,for example phthalic acid esters or oleic alcohol, are not as suitable.In order to counteract the above-mentioned unwanted effect ofplasticizers in borderline cases, a so-called “laking agent” may beincorporated in the binder-containing transfer layer to precipitate orrender insoluble any migrating pigments in order to prevent them frommigrating into and thus coloring the transfer layer applied. Suitablelaking agents are tannin and tannin derivatives. The laking agentspresent in inks and India inks may generally be used. They should bepresent in the binder-containing transfer layer in quantities ofpreferably about 0.5 to 5% by weight and, more preferably, about 1.5 to3.5% by weight, the range from about 2 to to 2.5% by weight being mostparticularly preferred.

[0029] To form the transfer layer, the particular binder selected ispreferably present in the form of an aqueous solution or dispersion. Inaddition, the additives discussed in the following are optionally added.The choice of a suitable solvent or dispersant will be determined by thetype of binder used. Suitable solvents/dispersants include in particularlow-boiling to medium-boiling organic solvents from the group ofalcohols, such as ethanol, isopropanol and butanol, ketones, such asacetone and methyl ethyl ketone, esters, such as methyl and ethylacetate, aromatic hydrocarbons such as toluene, aliphatic hydrocarbons,such as spirit with a boiling point of 70 to 140° C., either on theirown or in admixture, and more particularly water either on its own or inthe form of a mixture with low-boiling, water-soluble organic solvents.

[0030] The concentration of the binder in the solution or dispersion isnot critical to the invention. As an approximate guideline, it should bebetween about 3 and 15% by weight and preferably between about 6 and 12%by weight. To form the transfer layer, the solution or dispersion isapplied to the auxiliary support in a quantity of preferably about 15 to25 g/m² (dry weight) and, more preferably, about 18 to 22 g/m².

[0031] An advantageous component of the binder-containing transfer layeris a “stripping aid”. When the transfer layer is applied to a substrateunder conditions of tensile stress, the stripping aid ensures cleanstripping. Suitable stripping aids are cellulose derivatives, amongwhich the cellulose ethers soluble in organic solvents and/or water,such as methyl, ethyl, hydroxyethyl, ethylhydroxyethyl and carboxymethylcelluloses, cellulose esters, such as cellulose acetobutyrate andpropionate, are particularly preferred. Many other soluble cellulosederivatives which produce the required effects are also suitable. Thebasic cellulose skeleton in the soluble cellulose derivative is clearlyimportant whereas the groups introduced by the cellulose modificationmerely lead to an increase in solubility in the selected solvent.

[0032] For optimal formation of the transfer layer, the quantity ratioof stripping aid to binder is about 1:2 to 1:20 and preferably in therange from about 1:4 to 1:10.

[0033] The layer of pressure-sensitive adhesive may consist ofcommercial pressure-sensitive adhesives. These are elastic andpermanently tacky self-adhesive compositions with strong adhesion forceswhich adhere instantly to various surfaces at room temperature, evenunder light pressure. They are preferably applied in the form of anaqueous dispersion to the transfer layer and, optionally, interlayeralready present on the auxiliary support because the layers alreadyformed are not redissolved in this way. Pressure-sensitive adhesives ofthis type are, in particular, acrylate-based pressure-sensitiveadhesives. These starting materials may be viscous solutions anddispersions which are based on rubber, polyacrylates, polyvinyl ethersor polyvinyl isobutylene. Commercial materials based on polyacrylatesare preferred. Suitable commercial products are Ucecryl 913 and UcecrylPC 80 (marketed by ucb Dogenbos, Belgium) and polymer dispersion VP959/6 (marketed by Freihoff). The pressure-sensitive adhesive to beapplied, which is initially present in an aqueous medium, preferablycontains wetting agents or surfactants (marketed under the name Byk W).In version b) of the invention, a non-white pigment is finely dispersedin the solution or dispersion of the pressure-sensitive adhesive to beapplied. To form the layer of pressure-sensitive adhesive, thedispersion/solution of the pressure-sensitive adhesive, optionally withadditives, is applied to the transfer layer or additional layer in aquantity of preferably about 1 to 5 g/m² (dry weight) and, morepreferably, about 2 to 4 g/m².

[0034] According to the invention, the layer of pressure-sensitiveadhesive is preferably about 1 to 5 μm thick and, more preferably, about2 to 4 μm thick. The same range applies to the above-mentionedpolymer-bonded interlayer of version a). The white-pigmented transferlayer is preferably 15 to 25 μm thick and more preferably about 18 to 22μm thick. If the transfer layer were to be any thinner, productiondifficulties would arise or the functionality of the particular layerwould be affected. If the transfer layer were to be any thicker, nosignificant improvement would be obtained and unnecessary costs would beincurred. Also, a relatively thick tape cannot be used with the sameadvantage in a hand-held dispenser because, if the tape were too thick,the fixed volume of the cassette would inevitably mean a loss of tapelength.

[0035] The present invention is not subject to any significantlimitations in regard to the binders used for bonding the interlayer.The binders used in version a1) may be the same as those used in theformation of the white-pigmented transfer layer. Version a2) may evenuse those binders or polymers which are part of the layer ofpressure-sensitive adhesive. Reference is made in this connection to theforegoing observations.

[0036] The auxiliary support of the transfer tape according to theinvention preferably consists of a plastic film of the type normallyused for the supports of typewriter ribbons, for example of polyethyleneterephthalate, polypropy-lene, polyethylene, polyvinyl chloride orpolycarbonate. Silicone-coated paper has also proved to be a suitableauxiliary support. The silicone coating leads to a reduction in theadhesive tension between the binder-containing transfer layer and theauxiliary support. It may be replaced by other non-stick materials, forexample by polytetrafluoroethylene.

[0037] The auxiliary support is preferably about 10 to 16 μm thick and,more preferably, about 15 to 55 μm thick.

[0038] The above-described materials of the individual layers of thetransfer tape according to the invention generally satisfy the basicrequirement that, in the case of version a), the lowest adhesive tension(defined via the adhesion energy in accordance with Dupre's equation,Lit.: K. L. Wolf “Physik und Chemie der Grenzfläichen”, Springer Verlag1957, page 164) occurring in the transferlayer/interlayer/pressure-sensitive adhesive layer combination or, inthe case of version b), the adhesive tension between the transfer layerand the layer of pressure-sensitive adhesive is greater than theadhesive tension occurring between the auxiliary support and thetransfer layer. If this is not the case, a suitable non-stick layerwould have to be applied to the auxiliary support to satisfy this basicrequirement. The transfer layer formed on the substrate should not beadhesive to other materials coming into contact with it, i.e. on contactwith the hand or with paper. In the final analysis, therefore, thefollowing adhesive tension ratios are necessary for the successful useof the transfer tape according to the invention, the symbol “S” standingfor the adhesive tension ratio between the various materials: S₁paper/pressure-sensitive adhesive layer, S₂ weakest bond in the transferlayer/interlayer/pressure-sensitive adhesive layer combination, S₃transfer layer/auxiliary support, S₄ transfer layer/paper and S₅pressure-sensitive adhesive layer/(back of the) support. Numerousrequirements have to be satisfied in this regard: S₁ greater than S₃,S₂greater than S₃,S₅ far smaller than S₂ and S₅ smaller than S₃. Inaddition, the free surface of the transfer layer applied to a substrate,more particularly to paper, should not be adhesive on the outside, i.e.S₄ is zero or substantially zero. In addition, where the transfer tapeaccording to the invention is used in the form of a roll in a hand-helddispenser, this ensures that the pressure-sensitive adhesive layer showsan adhesion to the back of the auxiliary support which is weaker thanthe weakest adhesion in the transfer layer/interlayer/pressure-sensitiveadhesive layer combination and weaker than the adhesion between thetransfer layer and the auxiliary layer.

[0039] The transfer tape according to the invention is used withadvantage in dispensers which enable the transfer layer coated with thepressure-sensitive adhesive to be unrolled and, at the same time, theauxiliary support to be rolled up. This leads on the one hand toparticularly easy handling of the transfer tape according to theinvention. Commercial hand-held dispensers may be used. A so-called handroller is particularly suitable for this purpose. In hand rollers, aneasy-grip housing accommodates a feed spool with the transfer tape fromwhich it is guided over an application nib projecting from the housingand, from there, back to a take-up spool in the housing. A suitable gearbetween the two spools in the housing ensures that the transfer tape isalways under sufficient tension. To use the transfer tape, the userpicks up the dispenser and, by means of the application nib, presses the(removable) tape layer passing over its terminal edge onto the substrateto which it is to be transferred (for example a printed sheet of paperto make corrections). While applying pressure, the user moves thedispenser relative to the substrate and, in doing so, transfers forexample an opaque layer or a fluorescent layer to the substrate, theflexible auxiliary support being offwound from the feed spool and woundonto the take-up spool.

[0040] In the final analysis, the advantages afforded by the inventionlie in particular in the fact that a significant increase in coveringpower is achieved with the transfer tape according to the inventionwithout any of the disadvantages which would arise if the content ofdarkening pigments were to be increased in the white-pigmented transferlayer. Even where white-pigmented transfer layers are intentionallytoned down, a surprising effect is obtained by adopting the solutionproposed in accordance with the invention. In this case, too, coveringpowder is unexpectedly increased.

[0041] Technologically, the present invention may be explained asfollows but is not in any way limited to this explanation. In the priorart cited earlier, the transfer layer is also toned down. The effectsobtained may be explained by the fact that the relatively large whitepigment particles, more particularly titanium dioxide particles, areseparated from one another by sizeable empty spaces which allow lightbeams to pass through to a considerable extent onto the letters to bemasked so that they are not completely covered and show through. Thewhite pigments in question cannot be produced in significantly smallersizes at reasonable cost. The situation is different, for example, withcarbon black of which the particles can readily be produced in colloidalparticle sizes. By toning down the white-pigmented transfer layer, therelatively small carbon black particles are arranged in the empty spaceswith the result that the passage of light beams is at least limited.There are limits to any increase in the quantity of carbon black usedbecause the “whiteness” of the white-pigmented transfer layer isimpaired to an increasing extent. Now, it must be extremely surprisingto the expert that, in the absence of the darkening mentioned above,features a) and/or b) of the invention not only enable the desiredwhiteness of the white-pigmented transfer layer to remain substantiallyintact, they also increase the covering power of the transfer layer to asurprisingly favorable extent. This will be readily apparent to theobserver. The possibility of still toning down the transfer layer to aslight extent remains unaffected.

[0042] The invention is illustrated by the following Example:

EXAMPLE 1

[0043] The following aqueous dispersion is prepared for forming thewhite-pigmented transfer layer: Aqueous acrylate dispersion 23.42 partsby weight (25% in water; Worleecryl ® 7712W, a product of Worlee ChemieGmbH, Hamburg) Lactimon ®WS 0.8 part by weight (alkylammonium salts ofpolycarboxylic acids and polysiloxane copolymer) 2-Butoxyethanol 1.5part by weight Byk ®-034 0.2 part by weight (hydrophobic silicone-likecomponents in mineral oil) Byk ®-307 0.02 part by weight(polyether-modified dimethyl polysiloxane copolymer) Sorbitol 5.00 partsby weight Silica 4.00 parts by weight Titanium dioxide 35.00 parts byweight Ivory black 0.06 part by weight Aqueous dispersion of fine hollowbeads 30.00 parts by weight 100.00 parts by weight

[0044] The aqueous hollow-bead dispersion mentioned above is prepared asfollows:

[0045] 800 Parts by weight of Ropaque® Emulsion Op-62 LO-E commerciallyavailable from Rohm & Haas Company, Philadelphia, USA (consisting of anon-film-forming polymer with an effective solids content of 52% and anactual solids content of 37.5% and a pH value of 8.0 to 8.7 (particlediameter 0.4 μm, internal diameter 0.28 μm) are mixed with 176 parts byweight of water and 2 parts by weight of a defoamer (Byk®-034,hydrophobic silicone-containing components in mineral oil) and 22 partsby weight of a formic acid solution (prepared by mixing 100 parts byweight of conc. formic acid and 900 parts by weight of water). 30 Partsby weight of this acidified dispersion are used in the aboveformulation.

[0046] The above masking composition is knife-coated onto a siliconizedpaper support in a quantity of 18 g/m². The water is then evaporated offat about 80° C. by passing warm air over the paper support.

[0047] An aqueous dispersion consisting of the following components isthen knife-coated onto the surface of the transfer layer. Water 30.5parts by weight Colanylschwarz PR 130 0.5 part by weight (a product ofHoechst AG, carbon black content about 30%, rest water and dispersant =paste) Polymer dispersion VP 859/6 67.00 parts by weight (50% acrylatepressure-sensitive adhesive, a product of Freihoff) 25% Ammonia 2.00parts by weight 100.00 parts by weight

EXAMPLE 2

[0048] The procedure was as in Example 1 except that the followingformulation was used for the adhesive layer: Water 28.00 parts by weightAquasilber Aluminiumpaste LPW/1380 5.00 parts by weight (a product ofCarl Schienk AG; aluminium content 65%, water content 35%; particle size9 μm for an average of 50.3% of the particles) Lactimon WS 0.50 part byweight Polymer dispersion VP 859/6 65.00 parts by weight 25% Aqueousammonia 1.50 part by weight 100.00 parts by weight

1. A multilayer flexible transfer tape comprising an auxiliary supportand a layer of pressure-sensitive adhesive, a binder-containingwhite-pigmented transfer layer showing greater adhesion to the layer ofpressure-sensitive adhesive than to the auxiliary support being presentbetween the auxiliary support and the layer of pressure-sensitiveadhesive, characterized in that a non-white pigment is present in finelydispersed form a) in a resin-bonded interlay situated a1) between thewhite-pigmented transfer layer and the layer of pressure-sensitiveadhesive or a2) in the white-pigmented transfer layer, and/or b) in thelayer of pressure-sensitive adhesive.
 2. A transfer tape as claimed inclaim 1, characterized in that the inter-layer and/or thepressure-sensitive adhesive layer contain(s) at least about 0.1 % byweight of non-white pigment.
 3. A transfer tape as claimed in claim 2,characterized in that the inter-layer and/or the pressure-sensitiveadhesive layer contain(s) about 0.1 to 5% by weight and, moreparticularly, about 0.2 to 3.5% by weight of non-white pigment.
 4. Atransfer tape as claimed in any of claims 1 to 3, characterized in thatthe transfer layer contains fine-particle titanium dioxide as the whitepigment.
 5. A transfer tape as claimed in at least one of the precedingclaims, characterized in that the non-white pigment is a black pigment.6. A transfer tape as claimed in claim 5, characterized in that theblack pigment is carbon black.
 7. A transfer tape as claimed in any ofclaims 1 to 4, characterized in that the non-white pigment isfine-particle aluminium.
 8. A transfer tape as claimed in at least anyof the preceding claims, characterized in that the interlayer a) isabout 1 to 5 μm thick and, more particularly, about 2 to 4 μm thick. 9.A transfer tape as claimed in at least one of the preceding claims,characterized in that the white-pigmented transfer layer is about 15 to25 μm thick and, more particularly, about 18 to 22 μm thick.
 10. Atransfer tape as claimed in at least one of the preceding claims,characterized in that the pressure-sensitive adhesive layer b) is about1 to 5 μm thick and, more particularly, about 2 to 4 μm thick.
 11. Theuse of the transfer tape claimed in at least one of the preceding claimsin roll form in a hand-held dispenser.